Fluid filter cartridge and method of its construction

ABSTRACT

An insert for placement between concentric cylindrical filter elements comprises in a one-piece construction a tubular cylindrical body and pairs of parallel slits in the body each forming therebetween a strip of material connected to the remainder of the body at the ends of the strip. The strips are bowed inwardly away from the remainder of the body between their ends to form protrusions extending transversely from the remainder of the body.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 288,339 abandoned, and160,906 (now U.S. Pat. No. 4,317,727) filed July 30, 1981 and June 18,1980.

BACKGROUND OF THE INVENTION

This invention relates to fluid filtering and, more particularly, to aninsert for a filter cartridge and its method of construction.

One type of filter cartridge in common use employs inner and outerconcentric cylindrical filter elements separated by an annular region.The cartridge is mounted in a housing having an inlet communicating withthe outer surface of the outer filter element and the inner surface ofthe inner filter element and an outlet communicating with the annularregion. Fluid flows radially inward through the outer filter element andradially outward through the inner filter element to the annular regionand then flows axially through the annular region to the outlet. Aproblem of the described filter cartridge is the tendency of its filterelements to collapse toward the annular region due to the opposingforces exerted thereon by the inlet pressure. This tends to restrictfluid flow to the outlet and to reduce the useful life of the filterelements.

U.S. Pat. No. 3,988,244 teaches the use of a so-called fluid carrierelement in the annular space between concentric filter elements in theform of a molded plastic mesh or netting wound about itself severaltimes. The carrier element completely fills the annular region so as tofunction as a spacer in preventing collapse of the filter elements andpermits transverse and axial fluid flow through the annular region byvirtue of the openings in the mesh or netting.

SUMMARY OF THE INVENTION

One aspect of the invention is a tubular, preferably single-ply, insertdisposed in the annular region between concentric inner and outer filterelements of the above-described type of filter cartridge. The insert hasa side wall, perforations formed in the side wall to permit transverseflow through the insert from the filter elements to the annular region,and protrusions extending transversely from the side wall to permitlongitudinal flow through the annular region; the side wall and theprotrusions together form a spacer between the filter elements.

Another aspect of the invention is a method of constructing a fluidfilter cartridge. A first annular pleated filter element having a smalldiameter is placed inside of a second annular pleated filter elementhaving a large diameter so the elements are concentrically arranged withan annular region therebetween. Partial openings are cut in the sidewall of a tubular insert, leaving flaps attached to the remainder of theside wall, and the flaps are permanently deformed away from theremainder of the side wall. The insert is placed in the annular region.The first and second elements and the insert are attached together toform a filter cartridge.

The described insert can be cheaply fabricated and provides a uniformlylow, transverse, and axial flow resistance in the region between thefilter elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of specific embodiments of the best mode contemplated ofcarrying out the invention are illustrated in the drawings, in which:

FIG. 1 is a side sectional view of a fluid filter assembly incorporatingthe principles of the invention;

FIG. 2 is a perspective view of the insert shown in FIG. 1;

FIG. 3 is a top sectional view of a portion of the insert of FIG. 1taken through plane 3--3 of FIG. 2;

FIG. 4 is a side sectional view of a portion of the insert of FIG. 1taken through plane 4--4 in FIG. 3;

FIG. 5 is a schematic view illustrating how the insert of FIG. 1 isfabricated;

FIG. 6 is a top sectional view of a portion of an alternative embodimentof the insert;

FIG. 7 is a side sectional view of a portion of the insert of FIG. 6taken through plane 7--7 in FIG. 6;

FIG. 8 is a top sectional view of a portion of another alternativeembodiment of the insert of FIG. 1;

FIG. 9 is a side sectional view of a portion of the insert of FIG. 8taken through plane 9--9 in FIG. 8; and

FIG. 10 is a perspective view of a portion of the inside of the insertof FIG. 8.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The filter assembly of FIG. 1 is, with the exception of an insert 10,constructed in the manner described in U.S. Pat. No. 3,988,244, thedisclosure of which is incorporated fully herein by reference. An inlet12 and an outlet 14 are formed in a base 16. Base 16, together with adome-shaped cover 18, forms a housing for a filter cartridge 20.Cartridge 20 comprises an annular, preferably cylindrical, pleated paperfilter element 22 having a large diameter and an annular, preferablycylindrical, pleated paper filter element 24 having a small diameter.Filter elements 22 and 24 are concentrically arranged with an annularregion 25 therebetween filled by insert 10. Absent uniformly spacedsupport by insert 10, the pleats of elements 22 and 24 tend to collapseon each other and to bunch up, due to the pressure difference across thefilter assembly in operation. A central passage 23 through cartridge 20is defined by the inner surface of filter element 24. A rigid upperannular retaining plate 26, which has a central aperture 27, covers theupper ends of filter elements 22 and 24 and annular region 25. A rigidlower annular retaining plate 28, which has a central aperture 29,covers the lower ends of filter elements 22 and 24. Retaining plate 28has a plurality of annular apertures 30 providing an exit from annularregion 25. A strap 32, which is attached to cover 18, serves to seatfilter element 20 on base 16 when cover 18 is in place so that centralpassage 23 lies in sealed communication with inlet 12 and annularapertures 30 lie in sealed communication with outlet 14.

In operation, as illustrated by the arrows, part of the fluid enteringinlet 12 flows radially outward from central passage 23 through filterelement 24 to annular region 25 and part of the fluid flows throughcentral passage 23 to the outside of cartridge 20 and then radiallyinward through filter element 22 to annular region 25. From annularregion 25, the fluid flows axially to outlet 14.

As depicted in FIGS. 2, 3, and 4, insert 10 comprises in a one-piece,preferably single-ply, construction a tubular cylindrical body 34 andprotrusions extending transversely from the side wall of body 34 in theform of inwardly bowed strips of material 36. Strips 36 are formed byparallel slits in the side wall of body 34, leaving strips 36 connectedto the side wall at their ends. The outer surface of the side wall ofbody 34 abuts the inner surface of filter element 22 and the innersurface of strips 36 abuts the outer surface of filter element 24. Thus,insert 10 serves as a spacer to hold filter elements 22 and 24 apartdespite the opposing forces exerted thereon by the pressure difference.As illustrated in FIG. 2, strips 36 follow a helical path around theside wall of body 34. As illustrated in FIG. 4, adjacent strips 36 arelaterally spaced from each other by portions 38 of the side wall of body34. Each pair of parallel slits, together with strip 36, formed therebydefines an aperture 40 for radial flow of fluid from filter element 22into annular region 25. Fluid is free to flow radially outward fromfilter element 24 into annular region 25 in the regions of insert 10where strips 36 are connected to the side wall of body 34. Asillustrated in FIGS. 2 and 3, strips 36 are arranged in staggered rowsand columns so vertically, i.e., axially, adjacent strips 36 areoverlapping to equalize axial flow resistance around the annular region.By staggering and overlapping vertically adjacent strips 36, the filterpleats of elements 22 and 24 are supported at approximately uniformlyspacing over their entire surface area facing annular region 25, therebypreventing collapse or bunching of the filter pleats. Strips 36 thusserve as effective spacers between filter elements 22 and 24 thatpresent a uniformly small axial and radial flow resistance.

Insert 10 could be fabricated by a punch and die operation fromcommercially available thin walled plastic PVC pipe; for example, pipewith a 6" diameter and 1/16" wall thickness. As illustrated in FIG. 5,the side wall of a blank 42 in the form of PVC pipe is clamped between arotatably driven punch wheel 44 and a die wheel 46. Punch wheel 44 hastwo circumferential rows of bowed cutting teeth 48 for cutting parallelslits in the side wall of blank 42 and permanently deforming the flapsof material formed thereby radially inward to form strips 36 of insert10. Each row of teeth 48 is arranged in a circle around wheel 44 andlies in a plane perpendicular to the axis of blank 42. Teeth 48 havesharp side edges for cutting the parallel slits in the side wall ofblank 42 and ends merging into wheel 44 so the flaps of material remainconnected to the side wall of blank 42 at their ends. Die wheel 46,which is freely rotatable, has two circular grooves 50, which arealigned with teeth 48. Blank 42 is supported manually by a guide, notshown, so it is fed between wheels 44 and 46 with its axis at a smallangle, i.e., 10° to 15°, with the vertical plane in which the axes ofwheels 44 and 46 lie. This causes teeth 48 to traverse a helical patharound blank 42. The axis of blank 42 lies in a plane perpendicular tothe vertical plane. As punch wheel 44 is rotatably driven, blank 42 anddie wheel 46 rotate and blank 42 translates axially, while teeth 48enter grooves 50, thereby cutting the deforming blank 42 to form insert10.

In a typical embodiment, strips 36 would have a length of between 3/4in. and 11/8 in. and a width of between 3/16 in. and 1/4 in.; thespacing between the outer surface of the side wall of body 34 and theinward facing surface of strips 36 is 3/8 in.; the spacing betweenadjacent strips 36 is 3/16 in.; and the spacing between strips 36 of arow is 3/16 in. These dimensions may, of course, vary with theconditions.

To construct filter cartridge 20, insert 10 is first fabricated in themanner described above in connection with FIG. 5. Next, filter element24 is placed into filter element 22 so the elements are arrangedconcentrically with annular region 25 therebetween. Then, insert 10 isplaced in the annular region. Finally, filter elements 22 and 24 andinsert 10 are attached together by bonding retaining plates 26 and 28 tothe ends of filter elements 22 and 24.

An alternative embodiment of insert 10 is shown in FIGS. 6 and 7. Atubular body 52 has a side wall with annular corrugations which serve asspacers for the concentric filter elements and channels for transverseflow through annular region 25. Perforations 54 are formed in the sidewall of body 52 midway between the crests of the corrugations to permitaxial flow through annular region 25.

Another alternative embodiment of insert 10 is shown in FIGS. 8 and 9. Atubular body 56 has cuts producing a plurality of rows of flaps, i.e., arow of flaps in the form of louvers 58 and apertures 60, a row of flapsin the form of louvers 62 and apertures 64, a row of flaps in the formof louvers 66 and apertures 68, etc. Louvers 58, 62, and 66 have oneedge connected to the side wall of body 56 and an opposite edgeextending transversely therefrom. Preferably, the louvers in each roware wider than the spacing between circumferentially adjacent louvers inthe row to permit overlapping and louvers in axially, adjacent rows arestaggered (i. e., louvers 58 with respect to louvers 62 and louvers 62with respect to louvers 66) and overlapping in analogous fashion tostrips 36 so as to equalize axial flow resistance around the annularregion and uniformly space the filter pleats of elements 22 and 24.Thus, louvers 58 serve as spacers between the concentric filter elementsand apertures 60 permit radial fluid flow from the filter element to theannular region.

The described embodiments of the invention are only considered to bepreferred and illustrative of the inventive concept; the scope of theinvention is not to be restricted to such embodiments. Various andnumerous other arrangements may be devised by one skilled in the artwithout departing from the spirit and scope of this invention. Forexample, the described insert could be employed to space a single filterelement from an impervious annular element as depicted in FIG. 4 of U.S.Pat. No. 3,988,244. Although it is preferable to use a single-plyinsert, some features of the invention are applicable to multiple-plyinserts. Strips 36 could extend all the way to the end of body 34instead of as shown in FIG. 2.

What is claimed is:
 1. A filter cartridge comprising:an inner annularelement; an outer annular element concentrically spaced from the innerelement to form an annular region at least one of the elementscomprising a pleated filter; an annular spacer insert concentricallydisposed in the annular region; a first annular retaining member withcovering one end of the first and second annular elements and theannular region; and a second annular retaining member covering the otherend of the inner and outer annular elements openings being formed in thesecond retaining member to provide an exit from the annular region, theimprovement characterized in that the spacer insert is a single-plytubular body with a sidewall, perforations formed in the sidewall topermit transverse flow through the body from the pleated filter to theannular region and protrusions extending transversely from the sidewallto permit longitudinal flow through the annular region, the sidewall andthe protrusions together serving as the spacer.
 2. The filter cartridgeof claim 1, in which both the inner and outer elements comprise pleatedfilters.
 3. The filter cartridge of claim 1, in which the perforationscomprise pairs of parallel slits each forming therebetween a strip ofmaterial connected to the sidewall at the ends of the strip, the stripsbeing bent away from the sidewall between their ends to form theprotrusions.
 4. The filter cartridge of claim 1, in which the stripsextend inwardly away from the sidewall.
 5. The filter cartridge of claim1, in which the strips follow a helical path around the sidewall.
 6. Thefilter cartridge of claim 1, in which adjacent strips are laterallyspaced from each other.
 7. The filter cartridge of claim 1, in which thestrips are arranged in staggered rows and columns to equalize axial flowresistance around the annular region.
 8. The filter cartridge of claim1, in which the perforations each comprise a cut in the sidewall of theinsert forming a louver with one edge attached to the insert and anopposite edge bent away from the sidewall of the insert to form theprotrusions.
 9. The filter cartridge of claim 1, in which the insert hasannular corrugations forming the protrusions.
 10. The filter cartridgeof claim 1, in which the perforations are located midway between thecrests of the corrugations.